Field of the Invention
Embodiments of the invention generally relate to an epicardial heart stimulator that stimulates a chamber or an antechamber, in particular that stimulates a right or left ventricle of a heart.
Description of the Related Art
Generally, implantable heart stimulators may include cardiac pacemakers. Such heart stimulators are generally connected to electrode lines, which have stimulation or defibrillation electrodes in a chamber of a heart or in the immediate vicinity. Typically, epicardial cardiac pacemakers do not require such electrode lines, but are implanted on the outer side of a heart and stimulate the heart tissue (myocardium) via a stimulation electrode attached to a housing. For example, World Intellectual Property Organization Patent Publication WO 2013152259, to Bar-Cohen et al., entitled “Minimally Invasive Epicardial Pacemaker”, appears to disclose an epicardial cardiac pacemaker with a stimulation electrode in the form of a helix.
Generally, a cardiac pacemaker may deliver an electric stimulation pulse to the muscle tissue (myocardium) of a heart chamber via the stimulation electrode so as to thus induce a stimulated contraction of the heart chamber, provided the stimulation pulse has a sufficient intensity and the heart muscle tissue (myocardium) is not in a refractory phase at that precise moment. So as to trigger a stimulated contraction of a heart chamber in this way, typically, stimulation electrodes having a relatively small surface area are usually used, since, in order to trigger a stimulated contraction of a heart chamber, it is sufficient for only a small part of the myocardium of this heart chamber to be stimulated initially. Such a stimulated contraction of a heart chamber may be referred to herein as a stimulated event. A natural contraction of the heart chamber may be referred to herein as a natural action or as an intrinsic event. A contraction for example of the right atrium of a heart may be referred to herein as an atrial event, which for example may be a natural atrial event or, in the case of an atrial cardiac pacemaker, may also be a stimulated atrial event. Generally, (intrinsic) and stimulated left-ventricular and right-ventricular events may be distinguished in a similar manner.
Typically, with regard to the stimulation of a heart chamber, in particular of the right or left ventricle of a heart, it should also be noted that these occur preferably atrium-synchronously so as to reproduce the natural contraction sequence of the heart as effectively as possible. Generally, there is initially a contraction of the right atrium and then, following an atrio-ventricular conduction period, there is a contraction of the right ventricle and, at the same time or shortly after, of the left ventricle. Under certain conditions, typically, the natural contraction of the ventricle is absent in some patients subsequent to a natural contraction of the atrium. In typical dual-chamber pacemakers, the natural contraction of the atrium is therefore detected as an intrinsic atrial event and stimulates the right and/or the left ventricle following a predefined conduction time.
Generally, the detection of such natural (intrinsic) events is achieved by sensing, such as measuring, the electric potentials of the myocardium of the respective heart chamber with the aid of sensing electrodes, which are part of a corresponding electrode line in the case of conventional heart stimulators.
Typically, the detection of intrinsic events in the ventricle makes it possible, for example, to operate a ventricular heart stimulator in demand mode, in which the delivery of ventricular stimulation pulses is then always suppressed when a natural ventricular event is detected within a respective time window. Generally, the detection of intrinsic events in the atrium makes it possible, for example, to deliver ventricular stimulation pulses (provided these are not suppressed) to a ventricular heart stimulator atrium-synchronously, for example after a predefined atrio-ventricular delay period following detection of the respective atrial event.
Typically, the stimulation modes that may be implemented with a heart stimulator may include VVI, VDD, DDD, etc.
Generally, epicardial heart stimulators may be implanted at 4 different positions, depending on which heart chamber or antechamber is to be stimulated, for example left- or right-ventricular or left- or right-atrial.